1. Field of the Invention
The present invention relates to an optical fiber and a method for forming an optical fiber and, more particularly, to an optical fiber cable having a flat tape-like configuration including a plurality of optical fibers arranged in parallel to each other and abutted to the adjacent one, hereinafter referred to as “tape-like fiber cable” and a method for treating or forming a terminal face of the optical fiber of such a tape-like fiber cable.
2. Description of the Related Art
FIGS. 4(a) and 4(b) are plan and side views illustrating a general structure of a conventional tape-like optical fiber cable, in which a plurality of optical fibers are arranged in parallel to each other and each is also mutually adhered to the adjacent fiber. Each fiber includes a lead 12 (optical fiber including a core portion and a cladding portion, hereinafter referred to as “lead”) and a cover 14 for covering the lead 12. In the example shown in FIG. 2, the tape-like fiber cable 10 is used as a collimator for emitting a parallel luminous flux from a terminal face of a lead 12. Also, a terminal face of the “graded index optical fiber” (GI optical fiber) 12b having a certain length is fused to the terminal face of the lead 12 which is a single mode optical fiber 12a. 
Such a conventionally known tape-like fiber cable is disclosed, for example, in Japanese Unexamined Patent Publications Nos. 4-25805 and 6-186501.
In the fiber cable used as a collimator, the terminal face of the lead 12 is formed as an inclined surface 12c with respect to the optical axis in order to reduce the optical return loss at the terminal of the optical lead.
In this tape-like fiber cable 10, the terminal face 12c of the lead 12 is an inclined surface which is inclined downward with respect to the plane in which the tape-like fiber cable 10 is arranged. In other words, the light emitted from the lead 12 travels in a direction (upward) to cross the plane in which the tape-like fiber cable 10 is arranged. Therefore, if a pair of such tape-like optical cables are used to form an optical device, as shown in FIG. 5, the tape-like fiber cables must be arranged so that the terminal faces thereof are inclined upward and downward, respectively. This is because, when the light passes through the inclined surface, the light is refracted because the terminal faces of the leads 12 are inclined with respect to the optical axis.
In order to make an optical device in such a manner that the light emitted from the lead travels in the same plane as that the tape-like fiber cable is arranged, as shown in FIG. 6, the terminal faces of the leads 12 of the respective fibers are formed so as to be inclined by a common angle θ for the end surfaces of all of the leads 12, such as disclosed in Japanese Unexamined Patent Publication No. 2001-324647. In this tape-like fiber cable, in the same manner as the tape-like fiber cable is shown in FIGS. 4(a) and 4(b), the leads 12 of the tape-like fiber cable are supported by a jig and the angle of the jig is controlled in such a manner that the terminal faces of the leads 12 of the respective fibers can be ground to be inclined by a certain angle
However, as mentioned above, if the tape-like fiber cable shown in FIGS. 4(a) and 4(b) is to be incorporated in an optical device, it is necessary to support the tape-like fiber cable 10 using a support 16 such as that shown in FIG. 5. Therefore, positioning of the tape-like fiber cable 10 is very difficult and manufacturing of such a support 16 is also very difficult.
On the other hand, as shown in FIG. 6, if the tape-like fiber cable is constituted to be arranged in a plane, it is relatively easy to incorporate the tape-like fiber cable into a device. Nevertheless, if the tape-like fiber cable is to be used for a collimator tape fiber, it is very difficult to accurately arrange that the GI optical fiber 12b has a precise predetermined length and, therefore, a necessary function as a collimator may not fully be attained.
The function as a collimator can be obtained by controlling the length of the GI optical fiber 12b to ¼ of the wave length or to a cardinal number of times thereof. However, as shown in FIG. 6, if a grinding operation was conducted in such a manner that terminal faces of all leads be cut at a common angle of θ, the length of the respective GI optical fibers 12b would not be uniform. It is required that the accuracy in the length of GI optical fiber 12b must be less than several Am and, therefore, the tape-like optical fiber cable as shown in FIG. 6 is not appropriate to use as a collimator. In addition, in the tape-like optical fiber cable as shown in FIG. 6, when the GI optical fiber 12b is fused to the lead 12, it may be possible to regulate the position where the GI optical fiber 12b is fused to the single mode optical fiber 12a, in consideration of the finished length of the GI optical fiber 12b. However, such a method is very complicated and it would be very difficult to precisely form the optical fibers.